The present invention relates to the provisioning of enhanced 911 service in a wireless communication environment and, more particularly, to the additional capability of locating potential witnesses in terms of other cell phone users, in response to certain cell phone-based 911 calls.
Wireless telephones have received wide acceptance for use in cellular systems, as well as in wireless user premises equipment applications. There are new cellular telephone systems under development, as well as wireless personal communication systems (PCS) for both the licensed and unlicensed bands. A cellular telephone or cell-like communication system involves a network of fixed base stations that provide an integrated communication service to a plurality of mobile transmitter/receiver (xe2x80x9ctransceiverxe2x80x9d) units, e.g., cellular telephones. The communications network attempts to communicate with each transceiver from the base station that provides the optimal communication, such as in terms of signal level, clarity, etc. The optimal base station is usually, but not necessarily, the one nearest the mobile transceiver. To provide the optimal communications support, the network needs to locate the geographic position of the mobile only to the xe2x80x9croughxe2x80x9d level required to assign the proper base station.
This rough estimate of the location of a mobile has been a hindrance in extending the conventional 911 aspect of communication service to the mobile environment. When a user makes an emergency 911 call on a standard corded telephone, the location of the user is quickly determined since the physical location of the telephone is known and unchanging. In contrast, cell phone callers can xe2x80x9croamxe2x80x9d anywhere within the physical bounds of the entire system and, as result, xe2x80x9cpermanentxe2x80x9d geographic location information associated with the cell phone is meaningless.
Based on this realization, the FCC has defined an xe2x80x9cEnhanced 911xe2x80x9d requirement which mandates that all wireless service operators must be able to provide geographic position data to Public Service Answering Positions (PSAPs) for E911 calls by October 2001. As a result of this mandate, wireless network operators connecting to the public switched telephone network must implement E911 service in two phases: Phase I stipulates that the system must pass the caller""s phone number, cell-site, and cell-sector location information through to a PSAP. Carriers were to complete this step by April 1998, but many are still in the implementation stage. Phase II presents the more challenging task (at least from a location technology standpoint), of providing the 911 caller""s location to the appropriate PSAP with an accuracy of 125 meters RMS (root-mean-square), in at least 67% of all cases. As most wireless operators proceed to fulfill Phase I requirements through their networks, they are also assessing which location technologies most effectively meet the Phase II requirements. These positioning methods are generally divided into two categories: (1) network-based systems that require some equipment installation at network base stations; and (2) handset-based systems that add GPS or another location technology to the wireless phone, but generally do not require additional network equipment.
Most network-based caller-location systems are based on time-difference-of-arrival (TDOA) or angle-of-arrival (AOA) measurements, or a combination of these two techniques. Cell-Loc provides one exemplary technology to determine the geographic position of mobile stations, as disclosed in U.S. Pat. No. 5,890,068, issued to M. T. Fattouche et al. on Mar. 30, 1999. In this case, receive-only antennas (ROAs) are located at base stations and TDOA measurements are made for various channel transmissions from mobile stations. This information is then used to determine the position of the devices, without requiring alterations to either the base stations or the mobile stations. In AOA technology, a set of receive-only phased array antennas are located at each base station and used to compute the angle at which signals transmitted from a mobile station arrive at the base station. See, for example, U.S. Pat. No. 5,786,791, entitled xe2x80x9cMethod for determining an angle of arrival of a signal transmitted by a remote unit in a communication systemxe2x80x9d, issued to E. J. Bruckert on Jul. 28, 1998. A disadvantage of both of these techniques is that the geographic position of a mobile station can only be determined when the mobile station is transmitting. An enhancement to these network-based techniques, referred to as RF fingerprinting, measures the distinct RF patterns and multipath characteristics of radio signals arriving at a cell site from a mobile unit, using this information to determine the mobile""s location with an additional level of granularity.
The FCC mandate clearly requires that wireless carriers be able to locate any caller requesting emergency assistance through its network. On the surface, this would appear to eliminate handset-based solutions, such as utilizing a Global Positioning System (GPS), from consideration since it would be essentially impossible to add GPS (or other location-sensitive components) to all phones operating on a network by October 2001. However, it is presumed that such a system could be phased in, with newer phones including the necessary technology. At a recent conference on wireless location system implementation, a Nokia representative reported that the company currently favors adding GPS to the handset as the best solution for caller location on CDMA networks. Ericsson has suggested a short-term solution based on TDOA and a long-term solution combining GPS in the phone with differential corrections, using a network server. In addition to manufacturing wireless phones, both Nokia and Ericsson supply wireless network infrastructure equipment. Lucent Technologies and Qualcomm, which also manufacture both wireless handsets and infrastructure equipment, report that they too are investigating long-term caller location solutions that include the addition of GPS to handsets. These wireless infrastructure suppliers generally favor GPS as an element of the long-term solution based on the view that aided-GPS will support a higher level accuracy will be needed to support a wide range of commercial location-based services. However, a number of major carriers continue to express a preference for a network-based solution.
Regardless of the technology ultimately deployed to provide the position location information of a mobile E911 caller, there are further aspects of this technology that may be deployed to provide additional features to such a system.
A need remaining in the prior art is addressed by the present invention, which relates to the provisioning of enhanced 911 service in a wireless communication environment and, more particularly, to the additional capability of locating potential witnesses in terms of other cell phone users, in response to certain cell phone-based 911 calls.
In accordance with the present invention, an off-line xe2x80x9cposition serverxe2x80x9d is added to the communication network and, upon receiving a request from a PSAP, will determine the identity and location of various other wireless communication devices in the vicinity of the 911 caller. Thus, in instances where it may be important to find witnesses (for an accident, a robbery, or the like), the stored location information associated with various other wireless devices in the network may be retrieved and those individuals contacted as potential witnesses.
In the practice of the present invention, an E911 agent at a PSAP will determine those calls which would benefit from xe2x80x9cwitnessxe2x80x9d information and then, on a case-by-case basis, launch a query to the position server to find and store this information (for later retrieval by the police, investigating entity, or other authorized individuals). The query includes a specific xe2x80x9cradiusxe2x80x9d and time/date in the request, such as xe2x80x9cfind all cell phone callers within a two mile radius of latitude 29xc2x0 E, longitude 110xc2x0 N at 2PM EDTxe2x80x9d. Since the information regarding the capability to locate each wireless device is being developed, the ability to store and then retrieve this information will be helpful in identifying people that can assist in various emergency situations.
In one embodiment of the present invention, the position server itself may contain a database for storing the location information of all mobile stations in the communication system. In this case, the position server directly searches the database for the identity of mobile stations that would satisfy a particular search request from a PSAP, and stores the results in a table in the position server.
In an alternative embodiment, a network element (such as a gateway element between the wireless network and a traditional PSTN) may store the location information for a set of mobile stations that communicates through that particular gateway (also referred to, for example, as a mobile switching center). In this arrangement, when the position server receives a request from a PSAP to locate potential witnesses for a 911 call (referred to in this discussion as a xe2x80x9csnapshot requestxe2x80x9d), the request is then forwarded to the relevant gateway elements that would be storing location information for mobile stations in the requested territory. Each gateway element then searches its own database and forwards the results to the position server, which then collects all of the incoming information and forms a xe2x80x9ctransaction tablexe2x80x9d, for that particular xe2x80x9csnapshot requestxe2x80x9d, the table storing all of the relevant information associated with the mobile stations in the vicinity of the 911 call.
In yet another embodiment, each mobile station may be equipped with an internal location buffer for automatically determining and storing the location of the mobile station at any given time. In this arrangement, when the position server receives a xe2x80x9csnapshot requestxe2x80x9d, the request is again forwarded to the relevant gateway elements (e.g., mobile switching centers), which then broadcast the request to all mobile stations in its serving area. The mobile stations then check their current geographic location information against the location information in the request, and forward their unique identity information to the network element if they are indeed in the relevant area of the search.
Other and further embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.